This invention relates in general to imaging, and more specifically to migration imaging and a process for erasing electrical latent images from migration imaging members.
Recently, a migration imaging system capable of producing high quality images of high density, continuous tone, and high resolution has been developed. Such migration imaging systems are disclosed in copending applications Ser. No. 837,780 and Ser. No. 837,591, both filed June 30, 1969 which are hereby expressly incorporated herein by reference. In a typical embodiment of the new migration imaging system an imaging member comprising a substrate with a layer of softenable material and electrically photosensitive particles is imaged in the following manner: a latent image is formed on the member, for example, by electrically charging the member and exposing it to a pattern of activating electromagnetic radiation such as light. Where the photosensitive marking material is originally in the form of a migration layer spaced apart from the substrate, material from the migration layer migrates imagewise toward the substrate when the member is developed by softening the softenable layer.
One mode of development entails exposing the member to a solvent which dissolves only the softenable layer. The photosensitive marking material (typically particles) which have been exposed to radiation migrate through the softenable layer as it is softened and dissolved, leaving an image of migrated particles corresponding to the radiation pattern of an original on the substrate with the material of the softenable layer substantially completely washed away. The particle image may then be fixed to the substrate. For many preferred photosensitive particles, the image produced by the above process is a negative of a positive original, i.e., particles deposit in image configuration corresponding to the radiation exposed areas. However, positive to positive systems are also possible by varying imaging parameters. Those portions of the photosensitive material which do not migrate to the substrate are washed away by the solvent with the softenable layer. As disclosed therein, by other developing techniques, the softenable layer may at least partially remain behind on the supporting substrate with or without a relatively unmigrated pattern of marking material complementary to said migrated material.
In another imaging member embodiment migration material is dispersed throughout the softenable layer in a binder layer configuration.
"Softenable" as used herein is intended to mean any material which can be rendered more permeable to migration material migrating through its bulk. Conventionally, changing permeability is accomplished by dissolving, melting, and softening as by contact with heat, vapors, partial solvents and combinations thereof.
"Fracturable" layer or material as used herein, means any layer or material which is capable of breaking up during development, thereby permitting portions of said layer to migrate toward the substrate in image configuration. The fracturable layer may be particulate, semi-continuous, or continuous in various embodiments of the migration imaging members.
"Contiguous", for the purpose of this invention, is defined as in Webster's New Collegiate Dictionary, Second Edition, 1960; "In actual contact; touching; also, near, though not in contact; adjoining."
In certain methods of forming the latent image, non-photosensitive or inert, fracturable layers and particulate material may be used to form images, for example, wherein an electrostatic latent image is formed by a wide variety of methods including charging in image configuration through the use of a mask or stencil; first forming such a charge pattern on a separate photoconductive insulating layer according to conventional xerographic reproduction techniques and then transferring this charge pattern to the imaging member by bringing the two layers into very close proximity and utilizing breakdown techniques as described, for example, in Carlson U.S. Pat. No. 2,982,647 and Walkup U.S. Pat. Nos. 2,825,814 and 2,937,943. In addition, charge patterns conforming to selected, shaped, electrodes or combinations of electrodes may be formed by the "TESI" discharge techniques as more fully described in Schwertz U.S. Pat. Nos. 3,023,731 and 2,919,967 or by techniques described in Walkup U.S. Pat. Nos. 3,001,848 and 3,001,849 as well as by electron beam recording techniques, for example, as described in Glenn U.S. Pat. No. 3,113,179.
The characteristics of the images produced are dependent on such process steps as charging, exposure and development, as well as the particular combination of process steps. High density, continuous tone and high resolution are some of the image characteristics possible. The image is generally characterized as a fixed or unfixed particulate image with or without a portion of the softenable layer and unmigrated portions of the layer left on the imaged member.
Within the framework of the discovery of this basic new migration imaging system, the present invention has been discovered which permits electrical latent image erasing, which includes the erasing of any prior history on said member, followed by the formation of a new electrical image on said member. This latent image erasure capability is much sought after when commercializing most any imaging system and especially a storage microimaging system which this migration imaging system lends itself so well to.